The present invention relates to a quenching apparatus used in conjunction with a quenching method for steel pipes which have been heated all over the length thereof to a given quenching temperature and more particularly in a conjunction with a quenching method so designed that during the cooling of a steel pipe, the pipe is rotated or the pipe is moved axially while rotating it and thus the whole pipe is cooled uniformly. This quenching apparatus can be incorporated as an in-line equipment in a steel pipe production line such that a steel pipe introduced from a preceding processing stage is quenched by the above-described quenching method and then the pipe is delivered automatically to the following processing stage, thereby uniformly cooling the pipe in the lengthwise direction and reducing the quenching time.
The quenching methods heretofore known for quenching steel pipes heated throughout the length thereof to a given quenching temperature include the following typical methods: (1) Outer surface quenching using ring nozzles; (2) inner surface quenching which sprays water from the end of a steel pipe; and (3) method of placing a steel pipe in a water tank and spraying a jet of water into the pipe from a nozzle positioned near the end of the pipe.
In this case, if a thick-walled steel pipe is quenched by the method (1), it is impossible to ensure a satisfactory cooling rate and moreover, due to variations in the amount of sprayed cooling water among the plurality of cooling water spray rings or among the ring peripheral positions or due to any misalignment between the central axis of the rings and that of a steel pipe to be quenched, the cooling rate of the steel pipe becomes nonuniform so that a warpage is caused in the pipe and this warpage, if large enough, not only causes inconvenience to the quenched steel pipe itself but also tends to cause damage to the quenching equipment. Also, the method requires a large quantity of cooling water. In the case of the method (2), while the required amount of cooling water is small as compared with the method (1), it is impossible to ensure a sufficient cooling rate for the quenching of thick-walled steel pipes and moreover any deflection in a steel pipe between its supporting beds has a considerable effect on the straightness of the steel pipe after the quenching. Further, the cooling rate is high on the entry side and low on the exit side with the result that the cooling rate becomes nonuniform in the lengthwise direction and this makes the quenching of long pipes difficult. While the method (3) has been devised to overcome the deficiencies of the methods (1) and (2), this method is also disadvantageous in that the nozzle provided inside the water tank is at some distance from the end of a steel pipe thus making it impossible to ensure a sufficient cooling water velocity within the pipe due to the resistance of the water in the tank, and that the upper and lower surface conditions of the steel pipe in the tank are not the same thus making it impossible to ensure uniform surface cooling of the pipe in both the lengthwise and circumferential directions. This fact is a decisive disadvantage for cooling steel pipes, particularly long pipes. Thus, all of the known methods present many difficulties.
Also, attempts have recently been made to incorporate a quenching apparatus in a steel pipe production line for online operation and thus a clamping device used with such quenching equipment is required that it is capable of operating at high speeds, clamping a steel pipe with its end face being pressed against the end face of a nozzle, clamping the pipe positively without the danger of the pipe being dislocated by the supply water or the like and so on. However, the clamping devices heretofore known in the art do not necessarily meet these requirements.
Another requirement is that steel pipes to be quenched vary in size ranging from small-diameter pipes to large-diameter pipes and these various pipes must be clamped in such a manner that the center of a pipe aligns with the center of the quenching head. In this case, while the method of holding the quenching head in place and vertically moving the supports of the pipe and the method of holding the supports of the pipe in place and vertically moving the quenching head are conceivable. However, due to a narrow range of vertical adjustments of the known equipment, it has been impossible to adapt them for steel pipes in a wide range of sizes and moreover the construction is complicated thus requiring troublesome arrangements and making it difficult to effect the desired alignment in a short period of time.